1. Field of the Invention
The present invention relates to a gear position detection system for a transmission. More particularly, the present invention relates to a gear position detection system which detects gear position, displays such information to the rider, and is protectively mounted in a manner that substantially shields a sensor from damage during operation.
2. Description of the Background Art
A conventional gear position sensor, on a foot-operated type transmission of a motorcycle or motor tricycle, is mounted on the outside of a transmission case side wall, at a shift drum shaft support portion thereof. A detection pin of the sensor penetrates through the side wall of the transmission case, so as to have its tip end contact a cam surface on an end face of the shift drum.
In the described conventional system, the mounting position of the gear position sensor is at a rear lower portion of a clutch, and in a depression defined between a projected portion of the transmission case, surrounding the clutch, and a vehicle body frame (see, for example, the disclosure of Japanese Patent Publication No. Sho 62-13537 (page 2, FIGS. 1 to 2)).
As shown in FIGS. 10 and 11, a shift drum 05 in the conventional foot-operated transmission, described in the above-mentioned patent reference, has a structure in which both end boss portions thereof are shaft-supported on a transmission case 04 integrated with a crankcase 03 of an internal combustion engine 0E.
In this known design, an engaging and stopping pin provided at the left end 05c thereof is engaged with and disengaged from a pawl 08a1 at the tip end of a shift arm 08, operated by a rocking operation of a gear-change pedal. When the gear-change pedal is rocked, the shift drum 05 is turned. This turning movement of the shift drum moves gears of a speed reduction gear train in the left-right direction through a shift fork 07, engaged with a plurality of (three) lead grooves 05b in the outer circumferential surface 05a of the shift drum. In this way, a gear change operation desired by the rider is achieved.
In the known arrangement shown in FIGS. 10–11, the gear position detector (sensor) 010 is mounted at a rear lower portion of the transmission case 04, due to the arrangement of the shift drum 05 on the lower side, relative to a main shaft and a counter shaft. The detector 010 is mounted on the outside of a side wall of the transmission case 04 at a shaft support portion thereof which supports a shaft of the shift drum 05. A detection pin 010a of the detector 010 extends through the transmission side wall, so as to contact with a cam surface 05g at an end face of the shift drum 05.
The gear position detector 010 is located at a rear lower portion of a clutch, in view of the constitution of the transmission, and the mounting position thereof is in a depression, defined between a projected portion of the case 04, surrounding the clutch, and the vehicle body, as shown in FIGS. 10 and 11.
In the drawing, symbol 0101 denotes a cable for the detector 010, which is connected to a display apparatus, such as an indication lamp, provided at a gauge panel (not shown) at a front portion of the vehicle body.
In a system in which the layout position of the shift drum is on the lower side, relative to the positions of the main shaft and the counter shaft provided in the transmission case, as described in the above-mentioned patent reference, the gear position sensor projects from the outer wall of the case, and is disposed in a depression between a projected portion of the case and the vehicle body, so that the sensor does not constitute an obstacle on the surface of the case, and so that the risk of contact, between a human body or other thing and the sensor, is reduced.
However, the depression defined between the projected portion of the outside wall of the transmission case surrounding the clutch, and the vehicle body is not necessarily a satisfactory mounting place for the sensor, because the projected portion of the case is very close to the mount portion of the sensor. Therefore, the projected portion constitutes an obstacle at the time of mounting the sensor to the case from the outside, and makes the mounting operation difficult to carry out.
On the other hand, where the position of the shift drum in the transmission case is selected at a higher location, relative to the main shaft and the counter shaft provided in the transmission case, the shift drum has such a positional relationship as to be contained within the outside diameter of the clutch as viewed sideways, and the shift drum is located substantially on the back side of the clutch as viewed sideways.
The selection of the layout position of the shift drum in such a positional relationship as to be contained within the outside diameter of the clutch makes it possible to provide a generally satisfactory place as the mounting position of the gear position sensor (detector) to be mounted in the projecting state, from the viewpoint of obviating the direct contact of a human body or other thing with the sensor, even where the sensor is in an exposed state.
However, while the selection of the higher layout position of the shift drum has merit, the selection, on the other hand, gives rise to complication of the mounting structure of the gear position sensor and difficulty in mounting the sensor. Specifically, in external mounting of the sensor after the clutch is mounted in position, that projected portion of the transmission case which surrounds the clutch constitutes an obstacle, and the available mounting space is very narrow, leading to difficulty in the mounting operation and requiring a specialized mounting structure.
In addition, checking of the mounted condition of the sensor by service personnel is made difficult, because the mounting position is on the sheer back side of the clutch as viewed sideways, and it is difficult to remove the sensor for maintenance and inspection thereof.
Although the known devices have some utility for their intended purposes, there is still a need to provide an improved location for mounting a gear position sensor on a transmission case, and for an improved sensor which has a mounting structure optimum for the selected mounting position, for solving the above-mentioned problems in the mounting of the gear position sensor in the background art. In particular, there is a need for an improved mounting location and sensor to solve the above-mentioned problems when the shift drum is disposed at a higher position relative to the main shaft and the counter shaft.